How to Load Test Your Battery

Want to know how to load test a car battery without a fancy tester? Your car has everything you need right on board to do the test without the use of a voltmeter or load tester. I have created this guide which will go over an easy step by step instruction process that will allow you to test your own battery while saving you money.

Here are the main reasons the unit will fail:

  • Battery is more than three years old
  • The alternator is not charging or overcharging the electrical system
  • There is a electrical (parasitic) draw on the system
To get started please watch the video below and then follow down the guide to see the additional information we have added on this subject.

If you are on the page because the engine will not start then you will need to do some checking first.

Learn more: Engine is not starting

If the battery warning light has been on while the engine is running then you need to test the alternator first because the battery might not be the problem because it is not getting recharged.

Learn more: Alternator testing

If you have a new battery and it goes dead overnight something in the electrical system is draining it down.

Learn more: Checking for an electrical draw

Now then, let's get started.

If the battery warning light is not on or gauge shows it the system it charging or the charging system checks out okay using a voltmeter let's continue.

A battery can fail in one of two ways, the first way is very quickly in others word you go out to your car and without warning it will just be dead. When this happens there isn't much you can do but wait for a tow truck or someone you know to boost the battery start using jumper cables. In this case a jump may not even help because the battery is so far gone it just dumps (pulls in) all the voltage supplied to it.

The second way the battery can go bad is a slow decline of voltage and amperage which gives you little signs along the way such so slow engine cranking in this case you will notice the starter sounding a little different. Once you notice this it's up to you to be preventive and change the battery before total failure occurs. The best way to confirm this is with the following test:

Step 1

When working with a battery wear protective eye wear and gloves, stand clear of the battery while the engine is being cranked over. Open the hood to locate the battery and check it's condition, you are looking for leakage and bulging which indicating warped internal plates that can short circuit and also corrosion which can eat the positive and negative cable away which will cause additional problems, these are all signs of problems.

Now, turn the headlights on and leave them on for about 15 minutes.

Step 2

After waiting and while the headlights are still on, try cranking the engine over while watching the headlight bulb brightness. The bulbs should only dim slightly when using the starter, if they dim way down and go out or you notice the engine is cranked over slowly followed by a machine gun style of clicking noise, the battery can not supply the voltage needed to operate and must be replaced. Learn more

If the unit was good it should be able to withstand this load test.

The electrical cables that supply power and ground can inhibit electrical flow, look for bulges near the top of the cable ends near the terminals. These bulges indicate corrosion expansion caused by the chemical reaction between the acid and copper wire inside the cable and should be replaced.

A non deep cycle battery must have a rest period or downtime to allow the plates inside time to cool. A battery subjected to constant charge and complete discharge will fail prematurely unless it is a deep cycle type unit. All batteries are a hazardous material and must be disposed of at a local parts store or recycle center.

If you have any questions about the information or testing, please visit our forum where thousands of answers have been given by our online mechanics. Learn more


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